Process of regenerating waste liquors from the manufacture of chrome pigments.



.of ten per cent. or more.

UNITED STATES PATENT OFFICE.

ALEXANDER S. RAMAGE,

OF DETROIT, MICHIGAN.

PROCESS OF REGENERATING WASTE LIQUORS FROM THE MANUFACTURE OF CHROMEPIGMENTS.

Specification of Letters Patent.

Patented'May 28, 1907.

Application filed March 27,1907. Serial 364,828.

To all whom it may concern:

Be it known that I, ALEXAN ER S; RAM- AGE, a citizen of the UnitedStates, residing at Detroit, in the county of Wayne and Stateof-Michigamhave invented-certain new and useful Improvements inProcesses of Regen eratingWaste Liquors .from the Manufacture ofOhromePigments, of which the following is a specification.

The object ofthis invention is to rovide a process by Which wasteliquors rom the manufacture of chrome pigments may be regenerated.

In the manufacture of chromates of lead, or yellow chromes, litharge isdissolved in acetic acid, the amount of acetic acid used depending uponwhether it is desired to produce abasic or neutral chroniate. For theproduction of the basic chromates, or orange shades, the proportion ofacetic acid is sufficient only. to yield basic acetate of lead, Whereasfor the production of the light shades, neutral acetateof lead isprepared. After the precipitation of the pigment by sodium bichromate,the clear liquor from the orange shades contains substantially all itsacetic acid in the form of sodium acetate, whereas the liquor from thelight chromes contains both sodium acetate and free acetic acid. Aschrome pigments are as a rule precipitated from weak solutions, theresulting liquors are highly dilute and the recovery of acetic acidtherefrom is correspondingly expensive. In common practice these liquorsare run to waste and constitute a large proportion of the expense ofmanufacturing chrome pigments. V 7

According to the preferred form of my in vention, there is added to suchdilute liquors a suflicient proportion of free acetic acid to restoretheir solvent power, and the, acidulated liquors are then utilized fordissolving fresh quantities of lead and precipitating the chromepigments in the usual manner. It is obvious that the liquors from theorange shades will require a greater proportion of acetic acid thanthose from the yellow shades. This process is repeated until sodiumacetate has accumulated in the liquor to the extent This liquor maycontain in addition to sodium acetate smaller proportions of free aceticacid and lead acetate, or of free acetic acid and sodium bichromate inaccordance with the character of the pigment last produced, an excess ofacetate of lead being present in the formation of the light shades and aslight excess of bichromate with the deeper shades; in the lat" ter casesufficient lead acetate is added to precipitate the chromic acid. Theresulting liquor will then be identical in composition with thatresulting from the precipitation of the lighter pigments. 4

To the liquor containing essentially sodium acetate, lead acetate, andfree acetic acid, soda ash or lime is added in proportion suflic'ient toprecipitate the lead. The liquor is then allowed to stand until theprecipitate settles and is then run off into' an evaporator, where it isconcentrated until it contains from twenty to thirty percent of sodiumacetate. The concentrated liquor is then run into a tank where it iscooled, usually by contactwith pipes conveying cold water. The quantityof sodium acetate in the liquor is then ascertained by test, andsufficient sulfuric acid is added to liberate a large proportion, sayabout ninety percent, of the acetic acid therein. The liquor is then.further cooled, say to thirty degrees Fahrenheit, at which point ninetypercent of the sodium sulfate separates out in crystalline form, leavinga liquor consisting essentially of acetic acid, some sodium acetate andsome sodium sulfate. -The mass is run through a hydro-extractor, thesodium sulfate crystals being washed with ice cold'water. crystals ofsodium sulfate depends upon the concentrationof the sodium acetatesolution to which sulfuric acid is added and uponthe rate ofcrystallization.

In practice it is preferred to produce comparatively large crystals, andthis is best ac- The size of the.

complished by concentrating the liquor to about twenty percent of sodiumacetate, adding sulfuric acid as described, and permitting thecrystallization to occur during a eriod of about eight hours. The sodiumsul ate crystals washed as above described can be dried in the'usualway, forming anhydrous sodium sulfate. In case the lead is precipitatedfrom the original liquor by means of lime, this so- IIC . practiceutilized for the preparation of fur tion of barium carbonate or othersuitable barium compound may be added, the precipitate in this casecomprising barium sulfate, or blanc fiXe, Which can be utilized in allcolor Works.

I claim:

1. The process of regenerating Waste liquors from chrome pigmentmanufacture which consists in concentrating said liquors, liberatingacetic acid therein by addition of sulfuric acid, separating sodiumsulfate by refrigeration, and utilizing the resulting acid solution forthe preparation of lead acetate.

2. The process of regenerating Waste liquors from chrome pigmentmanufacture which consists in concentrating said liquors, liberatingacetic acid therein by addition of sulfuric acid, separating a portionof the sodium sulfate by refrigeration, separating the remainingsulfuric acid by precipitation and utilizing the resulting acid solutionfor the preparation of lead acetate.

3. The process of regenerating waste liquors from chrome pigmentmanufacture Which consists in adding acetic acid to said liquors,dissolving a lead compound therein and precipitating a chrome pigment,repeating the operation to concentrate the alkali acetate in the liquor,concentrating the resulting liquor by evaporation, liberating aceticacid therein by addition of sulfuric acid, separating sodium sulfate byrefrigeration, and utilizing the resulting acid solution for thepreparation of lead. acetate.

4. The process of regenerating waste liquors fromchromepigmentmanufacture which consists in concentrating said liquors,liberating acetic acid therein by addition of sulfuric acid, separatingsodium sulfate by refrigeration, utilizing the resulting acid solutionfor the preparation of lead acetate, and precipitating a chromate oflead from said solution.

5. The cyclical process of regeiwrating waste liquors from chromepigment manufacture which consists in concentrating said liquors,liberating acetic acid therein by addition of sulfuric acid, seiiarating sodium sul fate by refrigeration, utilizing the resulting acidsolution for the preparation of lead acetate, precipitating a chromaticof lead from said solution, and utilizing the liquor in continuing theprocess.

6. The cyclical process of regenerating waste liquors from chromepigment manufacture, which consists in adding acetic acid to saidliquor, dissolving a lead compound therein and precipitating a chromepigment, repeating the operation to concentrate the alkali acetate,further concentrating the resulting liquor by evaporation, liberatingacetic acid therein by addition of sulfuric acid, separating a portionof the sodium sulfate by refrigeration, separating the remainingsulfuric acid by precipitation, utilizing the resulting acid solutionfor the preparation of lead acetate, precipitating a chromat'e of leadfrom said solution, and utilizing the liquor in continuing the process.

In testimony whereof, I allix my signature in presence of two witnesses.

ALFXAXDER S. RAM M 1 l l.

Witnesses:

FORD D. O. IliNenuAN, Anrnnn AslInY.

